The following information is provided to assist the reader in understanding technologies disclosed below and the environment in which such technologies may typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the technologies or the background thereof. The disclosure of all references cited herein are incorporated by reference.
The term “thrombogenicity” refers to the tendency of a material in contact with blood to produce a clot or thrombus. The term refers to both fixed thrombi and to emboli (which are thrombi which have become detached and travel through the bloodstream). The term “thrombogenicity” also encompasses events such as the activation of immune pathways and the complement system. Thrombosis and intimal hyperplasia are, for example, considered to be two primary reasons to result in implantation failure of implantable devices such as implantable vascular devices, including metallic stents and vascular grafts. Intimal hyperplasia is the thickening of the intima or innermost layer of a blood vessel as a complication of a procedure. It is a response of the vessel to injury. There have been a number of attempts at synthesizing “non-thrombogenic” implantable articles and devices, but problems persist.
For example, a number of current drug eluting vascular stents employ non-degradable polymers as drug reservoirs. Drug eluting stents exhibit reduced restenosis rates, and have gained market share as a result of their improved efficacy over non-coated stents. A problem associated with non-degradable polymeric coatings is the thrombogenicity encountered on those surfaces, which has been of particular concern later in the implant period, when anti-thrombotic management may not be as aggressive. Late stent thrombosis, where patients develop thrombotic complications much later than the normal early risk period, have been attributed to the tendency of these stents not to become endothelialized while presenting a relatively thrombogenic surface to the blood. While stents with biodegradable coatings generally appear to perform similarly to those with nondegradable coatings, there is little evidence that the biodegradable coatings employed to date have achieved marked reduction in thrombotic complication rates.